A MANUAL OF ZOOLOGY 49 



a good preservative for frogs. The abdominal wall must 

 be cut to alio* the liquid to gain access to the viscera. 



EXTERNAL ANATOMY— Notice the general shape 

 and attitude of the live specimen. Compare with a preserv- 

 ed specimen. Notice the color. Is there any variation 

 In coloi' on the same or different specimens? Reflect on 

 the mode of the frog and decide whether he is well adapt- 

 ed in form for his mode of living. In what respect would 

 the variations in color aid him in his life struggle? 



GENERAL STRUCTURE— The body as a whole con- 

 sists of an axial portion, iiead, and trunl<; and an appendi- 

 cular portion, the legs. What is the texture of the skin? 

 Notice whether or not the skin fits closely to the body. 

 Note the surface of the skin. Study the dorsal, ventral, 

 and lateral views of the head. Can you locate the divid- 

 ing line between the head and the body? Compare the 

 mouth of the frog and that of the lobster, as to position, 

 shape, and breadth of opening. Locate the eyes. Note 

 color and shape. Are the eyelids all alike? Note the diff- 

 erences if any. Has the frog the power to depress the 

 eyes? Keep this in mind and see If you can explain It 

 later. The brow-spot 'is between the eyes on a line con- 

 necting the anterior borders of the eyes. Th'e nostrils 

 will be found anterior to the eyes. Notice the position 

 and shape. Can they be closed? Is there any modifica- 

 tion of the skin around them? The tympanic membranes 

 are found posterior to the eyes. What is their shape? Do 

 they vary in size or color? Notice. the tension of this mem- 

 brane. To what is it fastened? Study the dorsal and the 

 ventral surfaces of the trunk to note any difference in 

 shape and in color. By' pressing the body between the 

 thumb and fingers note the hard parts or the skeleton. 

 Observe the hump that appears near the middle of the 

 back. By pressing your fingers ppstpriorly from this point 

 three hard ridges will be noticed. The two lateral ones 

 are the parts of the ilium. The middle one is the urostyle. 

 Find the anal opening at the posterior end. What is its 

 relative position to the posterior end of the urostyle? 

 Notice carefully the anterior legs. What is their direc- 

 tion? Can. the frog reach his nose with his hand? Does 



